# RCWeb Files App

The **RCWeb Files App** (`app/files`) is a distributed, real-time file sharing application within the RCWeb ecosystem. It demonstrates the **Symmetric Pattern**, enabling multiple users connected to the same virtual room to securely share and transfer files directly over a peer-to-peer style network without relying on central server storage.

![icon](pwa-512x512.png "Files App Icon")

## Screenshot
![screenshot](screenshot.png "Files App")

## What it does

- **Instant File Sharing**: Users can share files by dragging and dropping them into the browser window or using the file selection dialog.
- **Distributed Shared View**: As soon as a file is added locally, its metadata (name, size, proxy download link) immediately appears in the shared file list of every other participant in the room.
- **Direct Peer-to-Peer Transfers**: When a user decides to download a shared file, the file's data is transferred directly from the sharing user's browser in chunks. The server strictly acts as a relay buffer and does not retain the files.
- **State Synchronization**: If a new user joins the room, their app automatically requests the current list of shared files so they are immediately caught up with what is available.
- **Easy Room Access**: Generates a standard QR Code that users can scan with their mobile devices to instantly launch the app and join the current file-sharing room.

## How it works

The core logic resides in `script.js` and leverages the RCWeb `comms.js` communication framework.

- **UI Interaction & State**: Users add files via the native file input or drag-and-drop event listeners (`dragEnter`, `drop`). These local `File` objects are stored in the `files` array memory. The `promptExit()` function prevents accidental closing of the tab, which would sever the file streams.
- **Broadcasting File Availability**: When `broadcastFileList()` executes, the app dynamically constructs safe proxy URLs (e.g., `/x-file/room/client/fileId/fileName`). It creates a JavaScript string of `fs.addFileLink(...)` execution commands and broadcasts it via `rc.send(listJs, "files")`. When evaluated on remote peers, this updates their UI with download links.
- **On-Demand File Chunking**: Remote download requests trigger the `rc.sendFileChunk(fileId, start, url)` callback on the user who originally shared the file. The app slices the requested segment from the local `File` blob.
- **HTTP PUT Streaming**: The sliced portion is immediately uploaded to the RCWeb server relay using an `XMLHttpRequest` (XHR) HTTP `PUT` operation with specific headers (`Content-Type`, `Content-Range`) in `sendChunk()`.
- **Peer Discovery Integration**: The app listens to `rc.onUpdateClients(clients)`. Whenever a new participant emerges in the connection pool, it triggers `fs.requestRefresh()`. The room coordinates a debounced `fs.refresh()` cycle, ensuring the new entrant receives the full `broadcastFileList()` payload from all active seeders without spamming the network.